Electropolisher



ELECTROPOLISHER Charles A. Kienberger, Ralph E. Greene, Irving C."Flanders, and Arville R. Flynn, ak'-Ridge,-Tenn., as-

signors to the United States of America as represented by the United-States. Atomic Energy Commission Application June 21, 1949, Serial No.100,358

4 Claims. (Cl. 204-225) This invention relates to the "art of thepreparation of highly accurate or perfect surfaces on a material such asmetal, the metal to be used as a sample upon-which another metal such asuranium is plated for purposes of scientific analysis of the uranium orother metal for determining its isotopic content. The scientificanalysis may be a fission process of analysis. The sample upon which themetal to be analyzed 'is plated is usually in the form of a disc and maybe made of nickel for example. it has been found that the degree ofperfectuessof the surface of the metal disc, uponwhich the metal, suchas, uranium is plated for scientific analysis,'hasa-direct efiect uponthe precision and accuracy of-the scientific analysis. it has been foundthat there are verypronounced variations in the surfaces-of nickeldiscsobtainedifrom commercial'sources. Inorder to achievelhighlyaccurateresults intheanalysis for isotopic content f such material asuranium, it is necessary to minimizeor eliminate the variation in degreeof perfection of the surfaces of sample discs used.

This invention utilizes a process of electropolishingthe sample discsfor obtaining a uniformly reproduciblesurface on large quantities ofdiscs. Electropolishing is the reverse of electroplating, since themetal being polished is the anode and rapidly goes into solution. On thesurface or" the metal being polished, the highest current densitiesoccur at the peaks and projections'and. sharp edges and, therefore,these have a tendency to. go into solution before the remainder of thesurface. This causes asmoothing of the surface and, with the appropriatecombination of electrolyte and current density,.a mirror-like surfacecan be produced.

The primary objectofthe present invention is to, provide a simple,convenient, and effective device for electropolishing sample discs usingthe above describedprocess, rapidly, effectively, and uniformly. H v

Another object of the invention is toprovidea device as referred toabove, capable of withstanding the electrochemical action of theelectrolyte and the high current involved.

Another object of the invention is to provide an electropolisher forsample discs comprising an electrolyte container having a fiat anodetherein, a vertically reciprocable cathode holder 'irnmersable in theelectrolyte, the cathode embodying a shoe for carrying the sample discand the cathode holder being reciprocable into a position wherein thesample disc is broughtintopressure contact with the anode.

Another object of the invention is to provide an electropolishing devicecomprising a containerof electrolyte,-a horizontal anode-forming surfaceimmersed in said electrolyte, a vertically reciprocable cathode alignedwith said anode surface and said cathode embodying a holder for samplesto be electroplated, the cathode holder being movable in a direction tobringfthe sample intopres'sure contact with the anode surface. Furtherobjects and numerous other advantages of our invention will become 2apparent from the following detailed'description and annexed drawings,wherein- Figure'l is a'perspective view, partly cut away, of one formofour invention.

Figure 2 is a sectional view of the cathode and sample holder.

Figure? is a cross sec'tional view of the anode member.

Referring to Figureil of the'drawings, there is shown a frameconsistingof an h-shaped supporting arm 1 rigidly attached at -its'lowerend to a current-conducting base plate 2 andat its upper end'to-avertical, slotted, tubular holder 3. iSlidably' mounted in this tubularholder 3 is a cylindrical support 4 made of a current-insulatingmaterial (such as plastic). Ri'gidly-attachedto the support 4 is aninsulated handlle 5 which projects through'a slot 3a in the tubularholder 3. The slot 3a is of approximately the'same-width'throughout asthe diameter of the handle '5, thus preventing play'of the handle 5between the sides ofthe slot 3a;such play would be particularlyobjectionable when the handle 5 is in the lower, substantially lateral,part of the'slotfia. The lateral part of slot 3a has a slightdownward'slant forpurposes which will presently become apparent.

The center of the support 4 is hollowed'to permit the passage-of acurrent-conducting rod 6, about which the suppo'rt'4' can turn freely.'Both ends of the rod 6 are threaded. The topend of the rod-6-extendsout of the support 4 and through, respectively, a metal protector cap'7, a supporting "nut (indicatedat 8),-'a lug 9 connected to the.negative terminal of a directcurrent power supply (not shown), anda untl-0 for clamping the lug 9 in place. The lower: end of the rod 6 isthreaded into a tapped extension lla "of a 'current-conducting circularelectrode 11 forming a cathode as will be described. The extension llafits into'a recess provided in the lower end of the support=4;the'diameter of the'recess permits free turning ofthesupriorbdabout theextension 11a.

The circular base .of .the electrode 11 has a diameterslightlylarger'than' that-of the nickel discs to be polished.Rigidly'attached to the underside of this base by three screws 12 tisaidiscsholding assembly composed of two aligned rings 13 and 14 made ofcurrent-insulating material such as 'fluorothene an'd held firmlytogether by two screws 15 as shown. "Passages for liquid and gas areprovided'in this assembly through the openings formed by-cut-awayportions'at the top edge of-the ring 13. A portion'of the lower edge ofthe top ring 13 is cut away was to form a slit 13a through whichspecimen nickel discs -may beinserted into the disc-holding assembly 13,Bland-'15. The internal diameter ofthe assembly is such that the rim'ofa completely-inserted disc iseverywhere supported :bythe ibottom ring14, as'shown in Fig. 2. The-lower-inner edge of ring-13- is bevelled asshown at 1315. The hole 16 provides easy'access for a tool used toinsert and remove the disc.

Beneath the disc-holding assembly 13, 14 and 15 is a container 17madeofcurrent-insulating material and containingan iacidsolutionconstituting anelectrolyte. In this container:17,and'centeredbeneath the disc-holding assembly 13, .14 and .15, :is a cylindricalelectrode assern bly, :thediameterof whichpermits the ring 14 to fitaround the 'assemblys -top "edge-whenthe disc-holding assemblyis loweredover it. As shownin'detail' in Fig. 3, tthe assembly consists of :aeurrent conducting electrode 18 .(Fig. 3) clampedto.acurrentdnsulatingcircular support 19 by a nut 26 screwed on a threaded extension 18a ofthe electrode 18 (Fig. 3).

-Thesu'rface of the electrode :18 (Fig. 3 which would be exposed .toztheacid solution in the container 17 is covered with a protectingsheet 21ofacurrent-conducting material (like platinum) which is resistant toelectrolytic decomposition. This protecting sheet 21 is softice solderedto the under-edge of the electrode 18 (Fig. 3). A circular depression21a is provided to take up slack in the sheet 21, permitting awrinkle-free surface on which the nickel discs rest. The remainder ofthe electrode 18 (Fig. 3) is protected from inleakage of solution by tworubber gaskets-one'(22) placed between the edge of the protecting sheet21 and theelectrode support 19, and the other gasket 23 placed betweenthe electrode support 19 and the container 17. The entire electrodeassembly (shown in detail in Fig. 3) is clamped to the container 17 andthe base plate 2 by a nut 24 screwed on the threaded extension 18a. Alsobolted to the base plate 2 is a cable 25 connected to the positiveterminal of the direct current power supply previously mentioned herein.The electrode assembly shown in Fig. 3 is thus an anode.

Owing to the corrosive nature of the electrolytic solution, theelectropolisher is preferably constructed throughout of materialsresistant to acid corrosion. In a desired construction of theelectropolisher, the negative cable, which is connected to lug 9 isanchored at some point near connection of the lug to the rod 6; thisprevents rotation of the rod 6, permitting the disc-holding assembly 13,14 and 15 to remain in one predetermined position during operation.Preferably, the supporting nut 8 is screwed down far enough on the rod 6to allow only a slight vertical play of the rod 6 in the support 4.

In a preferred use of the electropolisher, a solution of approximately70% sulphuric acid and 30% water (by weight) is placed in the container17, where it is cooled by water flowing through glass tubing 27. Then,after the electropolisher power supply is energized, a nickel disc isfitted into the disc-holding assembly 13, 14 and 15, and the handle 5 ismoved to the bottom of the vertical section of the slot 311. and theparts attached to it, as described, fitting the nickel disc against theupper surface of the protecting sheet 21 with sufficient pressure toforce the nickel disc upward against the previously described bevellededge 13b (Fig. 2) of the top ring 13. The bevelled edge 13b (Fig. 2)acts to center the nickel disc and to prevent its sliding out of theslit 13a. The handle 5 then is moved into the lateral portion of thebottom of the slot 3a and to the end thereof. The slightly downwardinclination of this lateral part of the slot 3a places a predetermined,additional pressure on the nickel disc to prevent arcing between thedisc and the protecting sheet 21. In practice this pressure has been asmuch as several hundred pounds.

The lateral movement of the handle 5 moves only the v free-turningsupport 4 and results in no twisting or wearing action on the nickeldisc or the protecting sheet 21. With the nickel disc thus positioned,it thus becomes the anode in the electrolytic circuit, its upper surfacebeing uniformly spaced from the cathode 11. The handle 5 is allowed toremain in the lower, lateral position in the slot 3a for approximatelytwo minutes, during which This lowers the support 4 r i 4 piece composedof chemically resistant conducting material. Again, the cable 25 couldbe connected directly to the threaded extension 18a, eliminating thenecessity of making the base plate 2 of current-conducting material. Itis intended that all such equivalents and such variations andalternatives as may occur to those skilled in the art shall fall withinthe spirit and scope of the claims appended hereto.

We claim:

1. An electropolisher for polishing one side of a substantially fiatmetal disc comprising a frame, a cathode support slidably mounted insaid frame, an electrolyte container placed in juxtaposition to saidsupport, an anode mounted in said container, a cathode having asubstantially fiat surface mounted on said support so that its surfaceis essentially parallel to the surface of said anode and in alignmenttherewith, means for holding a metal disc at a fixed distance from saidcathode, said support, anode, cathode, and disc-holding members having acommon vertical axis, and means for bringing said cathode within saidcontainer and for contacting the upper surface of said anode in pressurerelation with the lower surface of said disc.

2. A metal polishing apparatus comprising a tank containing anelectrolyte, an electrode immersed therein, a second electrode mountedin juxtaposition with said tank, an electrical insulator formingspecimen disc-supporting means and carried by said second electrode,means for simultaneously contacting said first electrode with saidspecimen and positioning said second electrode in said electrolyte inproper operative relation with said first electrode, and meansconnecting said first electrode to the positive side of a source ofpower and said second electrode to the negative side whereby said secondelectrode becomes a cathode and said specimen becomes an anode and byelectrolytic action a polishing effect is exerted on said specimen.

3. An electropolisher for metal discs comprising a slotted frame, asupport member slidably mounted in said frame, a handle rigidly fixed tosaid member and extending through an U-shaped slot in said frame, aconductor carried by said support, a cathode plate carried by saidconductor, a slotted hollow cylindrical insulator having side ports foringress and egress of electrolyte forming a disc holder and fixed tosaid cathode plate, an electrolyte container, an anode assemblyincluding a conductive, electrolyte-resistant sheet forming awrinklefree surface over a support member having a central depression,said assembly being disposed within said container and aligned with saidcathode and said disc holder, said handle and said slot being soarranged as to allow said support to move said holder and cathode intojuxtatime the nickel disc is subjected to an electrolytic polishk ingcurrent of approximately 36 amperes at a voltage of 12 to 15 volts. Atthe expiration of this polishing time, the handle 5 is raised to theposition shown in Fig. l and the polished nickel disc is removed. Thisprocedure is repeated for each disc polished. During operations, heatgenerated is carried away by cooling coil 27.

With the above procedure discs of mirror-like quality and gooduniformity have been produced at the rate of about twenty-five discs perhour. The amperage and time interval may of course be considerablyvaried; the

position with said anode and to contact one surface of a disc held insaid holder in pressure relation with said anode sheet.

4. The structure of claim 2 wherein said disc-supporting means comprisesa pair of aligned insulating rings containing cut away portions formingfluid ports and a slit adapted to receive a disk specimen.

References Cited in the file of this patent UNITED STATES PATENTS1,747,165 Eaton Feb. 18, 1930 2,323,952 Wick July 13, 1943 2,349,908 LaMotte May 30, 1944 2,372,567 Graham et al Mar. 27, 1945 2,378,002Drummond et al June 12, 1945 2,399,254, Rieger Apr. 30, 1946 2,475,586Bartlett July 12, 1949 FOREIGN PATENTS 350,658 Great Britain June 18,1931

1. AN ELECTROPOLISHER FOR POLISHING ONE SIDE OF A SUBSTANTIALLY FLATMETAL DISC COMPRISING A FRAME, A CATHODE SUPPORT SLIDABLY MOUNTED INSAID FRAME, AN ELECTROLYTE CONTAINER PLACED IN JUXTAPOSITION OF SAIDSUPPORT, AN ANODE MOUNDTED IN SAID CONTAINER, A CATHODE HAVING ASUBSTANTIALLY FLAT SURFACE MOUNTED ON SAID SUPPORT SO THAT ITS SURFACEIS ESSENTIALLY PARALLEL TO THE SURFACE OF SAID ANODE AND IN ALIGNMENTTHEREWITH, MEANS FOR HOLDING A METAL